Paper No. 5
Presentation Time: 8:00 AM-6:00 PM
Very Late Frasnian (Upper Devonian) Brachiopod Fauna of the Theodossia Scopulorum Zone in the Paleoequatorial Mackenzie Shelf (Northwest Territories-Canada) - Western Laurussia
The Theodossia scopulorum Zone is an informal Upper Devonian interval described by Raasch (but never formally defined) to include the youngest Frasnian carbonate platform shelly faunas in the upper Mackenzie River Valley region and Canadian Rocky Mountains of central and western Alberta and eastern British Columbia. Deposits of the Kakisa Formation in the upper MacKenzie River Valley region yield well preserved shelly faunas of scopularum Zone. The Kakisa is carbonate platform sequence package that accumulated in the paleoequatorial MacKenzie Shelf during Devonian T-R cycle IId-2. The conodont sequence in the Kakisa with brachiopods and corals of the scopulorum Zone are correlated with latest Frasnian Montagne Noire Zone 13. The scopulorum Zone fauna of western Canada comprises the survivor fauna of the initial late Frasnian Lower Kellwasser extinction bioevent in the northern Cordilleran continental margin of western Laurussia. In the outcrop belt along the Kakisa River and the upper MacKenzie River Valley the Kakisa is divided (in ascending order) into members 1 to 3. Skeletal shoal facies of Member 1 along the Kakisa River yield Theodossia (keeni & scopulorum), and distinctive species of Hypothyridina, Cranaena, Gypidula and Pseudoatrypa. Middle shelf skeletal packstones and wackstones of Member I in the Mackenzie River Valley yield species of Pseudoatrypa, Spinatrypina (Exatrypa), and Cyrtina. Subtidal platform facies of the middle Kakisa (Member 2) yield moderately diverse brachiopod assemblages dominated by Pseudoatrypa, with species of Cyrtina, Schizophoria (S.), Cyrtospirifer, Conispirifer, and Devonoproductus. The brachiopod fauna of the reefal facies of Member 3 in the Upper Kakisa includes species of Theodossia, Gypidula, Desquamatia (D.), Pseudoatrypa, Spinatrypa (S.), Conispirifer, Cyrtospirifer, and Craneana. None of the brachiopod species of the upper scopulorum Zone in Member 3 of the upper Kakisa are known from early Famennian post-extinction survivor faunas and were victims of the Upper Kellwasser extinction bioevent.